Empty Nests Support Group
Empty nest syndrome is a general feeling of depression and loneliness that parents/other guardian relatives feel when one or more of their children leave home. Empty nest syndrome has become more prevalent in modern times, as the extended family is becoming less common than in past generations, and the elderly are left living by themselves.

I'm not sure if you're looking for suggestions or if you just need to vent.
I've found a couple of things to be helpful. One approach I've successfully employed in the past is to talk with my kids and say "I love you but I am feeling sincerely disrespected. I want to be part of your life but it's essential that the respect go both ways." And I brought up specifics of the situation to demonstrate what was happening that I felt disrespected.
Alternatively, when a child has said they're not going to be here on a special day I've said, "Hey, no worries. I have plans that day anyway but would love to see you when we both have a free evening."
This second approach helps them realize I do have a life and other things I enjoy - that I have a full life and can enjoy things without them.
Sending hugs.